Verdu Montse1,3, Roman Ruth1, Calvo Miquel4, Rodon Natalia1, Garcia Beatriz1, Pujol Merce1 and Puig Xavier1,2,3.
1BIOPAT.Biopatologia Molecular, SL, Grup Assistencia, Barcelona, Spain; 2Hospital de Barcelona, SCIAS, Grup Assistencia, Barcelona, Spain; 3Histopat Laboratoris, Barcelona, Spain; 4Universitat de Barcelona(UB), Statistics Dpt., Barcelona, Spain;
Background: ERG gene rearrangement, detected by FISH or RT-PCR, has been identified as a highly specific alteration, present in 40-50% of prostate carcinomas (PCa). Recent studies describe a novel anti-ERG antibody, whose positive staining by immunohistochemistry (IHC) highly correlates with the ERG rearrangement. The standardization of an IHC assay would have significant diagnostic and prognostic value. Marked variations in rates of PCa among populations in the world suggest the involvement of genetic factors. The aim of this study was to identify the incidence of this rearrangement in a Spanish population and to test the specificity of the IHC ERG evaluation for PCa.
Design: Tissue microarrays (TMA’s) of a wide variety of normal and neoplastic tissues were tested. TMA’s were analyzed by IHC performed by ABC immunoperoxidase staining, using a rabbit monoclonal antibody (ERG, clone EPR3864). The expression of ERG protein was scored as negative, weak, moderate or strong, using vascular endothelial cells as internal control. A case was judged positive if any of the evaluable cores showed a positive staining, whichever its intensity.
Three prostate TMA’s were constructed using prostatectomy specimens, and their Gleason score (GS) and extent of invasion (pT) were routinely determined. These TMA’s included, besides samples of malignant cases (175), specimens with prostatic hyperplasia (25) and high grade prostatic intraepithelial neoplasia (HGPIN) (10).
In addition, TMA’s of the most common tumors in Spain (breast, colon, lung and bladder) were also tested (270 samples in total).
Results: In our study 44% (76/171) evaluable cases of PCa showed ERG expression, most of them presenting strong staining (61/76). No ERG expression was observed in any of the HGPIN samples, as reported by others. ERG expression was independent of GS (p=0.735) and pT (p=0.128). There was no ERG expression found in any other type of tumor, with the exception of one bladder cancer single sample which showed focal expression.
Conclusion: The frequency of ERG detected in our study correlated with that published in other Caucasian populations. The expression of ERG protein is exclusively detected on prostatic adenocarcinoma, corroborating the specificity of ERG rearrangement for these tumors. Thus, in addition to its prognostic significance, the use of ERG detection by IHC may be useful in routine practice to complement the panel of prostatic carcinoma.